This is a two to approximately four center, double-blind, randomized study in patients with coronary, cerebral or peripheral vascular disease who will continue to take their usual medication (patients on anticoagulants and antiplatelet agents other than aspirin are excluded form the study). Six groups of 15 patients will be enrolled. Within each group, three patients will be randomized to receive placebo and 12 to receive CT50352. Study drug for the first group will consist of 10 mg of CT50352 (or its placebo) administered as enteric coated tablets orally once a day for 14 days; subsequent groups will be enrolled to receive progressively higher dose levels. Other projected dose levels to be studied include 20, 30, 40 50 and 60 mg daily. Dose increments may be reduced depending upon tolerability and the pharmacodynamic results, in order to ensure the safety of the patients and to adequately characterize the dose-response relationship. In addition, the protocol may be amended to study higher dose levels, provided that this is supported by the safety profile. A fully pharmacokinetic and pharmacodynamic (platelet aggregation and receptor occupancy) profile will be obtained after the last dose of study drug. These will require a 3 to 4 night stay in the clinical study unit. Otherwise, the study will be an outpatient study.